Thermoplastic silicone elastomers formed from nylon resins

ABSTRACT

A method for preparing a thermoplastic elastomer is disclosed, said method comprising 
     (I) mixing 
     (A) a rheologically stable polyamide resin having a melting point or glass transition temperature of 25° C. to 275° C., 
     (B) a silicone base comprising 
     (B′) 100 parts by weight of a diorganopolysiloxane gum having a plasticity of at least 30 and having an average of at least 2 alkenyl radicals in its molecule and 
     (B″) 5 to 200 parts by weight of a reinforcing filler, 
      the weight ratio of said silicone base to said polyamide resin being greater than 35:65 to 85:15, 
     (C) 0.1 to 5 parts by weight of a hindered phenol compound for each 100 parts by weight of said polyamide and said silicone base, 
     (D) an organohydrido silicon compound which contains an average of at least 2 silicon-bonded hydrogen groups in its molecule and 
     (E) a hydrosilation catalyst, components (D) and (E) being present in an amount sufficient to cure said diorganopolysiloxane (B′); and 
     (II) dynamically curing said diorganopolysiloxane (B′), 
     wherein at least one property of the thermoplastic elastomer selected from tensile strength or elongation is at least 25% greater than the respective property for a corresponding simple blend wherein said diorganopolysiloxane is not cured and said thermoplastic elastomer has an elongation of at least 25%.

FIELD OF THE INVENTION

The present invention relates to a thermoplastic elastomer compositionwherein a silicone base and a hindered phenol are blended with apolyamide resin and a silicone gum contained in the base is dynamicallyvulcanized in the mixture.

BACKGROUND OF THE INVENTION

Thermoplastic elastomers (TPEs) are polymeric materials which possessboth plastic and rubbery properties. They have elastomeric mechanicalproperties but, unlike conventional thermoset rubbers, they can bere-processed at elevated temperatures. This re-processability is a majoradvantage of TPEs over chemically crosslinked rubbers since it allowsrecycling of fabricated parts and results in a considerable reduction ofscrap.

In general, two main types of thermoplastic elastomers are known. Blockcopolymer thermoplastic elastomers contain “hard” plastic segments whichhave a melting point or glass transition temperature above ambient aswell as “soft” polymeric segments which have a glass transition or meltpoint considerably below room temperature. In these systems, the hardsegments aggregate to form distinct microphases and act as physicalcrosslinks for the soft phase, thereby imparting a rubbery character atroom temperature. At elevated temperatures, the hard segments melt orsoften and allow the copolymer to flow and to be processed like anordinary thermoplastic resin.

Alternatively, a thermoplastic elastomer referred to as a simple blend(physical blend) can be obtained by uniformly mixing an elastomericcomponent with a thermoplastic resin. When the elastomeric component isalso cross-linked during mixing, a thermoplastic elastomer known in theart as a thermoplastic vulcanizate (TPV) results. Since the crosslinkedelastomeric phase of a TPV is insoluble and non-flowable at elevatedtemperature, TPVs generally exhibit improved oil and solvent resistanceas well as reduced compression set relative to the simple blends.

Typically, a TPV is formed by a process known as dynamic vulcanization,wherein the elastomer and the thermoplastic matrix are mixed and theelastomer is cured with the aid of a crosslinking agent and/or catalystduring the mixing process. A number of such TPVs are known in the art,including some wherein the crosslinked elastomeric component can be asilicone polymer while the thermoplastic component is an organic,non-silicone polymer (i.e., a thermoplastic silicone vulcanizate orTPSiV). In such a material, the elastomeric component can be cured byvarious mechanisms, but it has been shown that the use of a non-specificradical initiator, such as an organic peroxide, can also result in atleast a partial cure of the thermoplastic resin itself, thereby reducingor completely destroying ability to re-process the composition (i.e., itno longer is a thermoplastic). In other cases, the peroxide can lead tothe partial degradation of the thermoplastic resin. To address theseproblems, elastomer-specific crosslinkers, such as organohydrido siliconcompounds, can be used to cure alkenyl-functional silicone elastomers.

Arkles, in U.S. Pat. No. 4,500,688, discloses semi-interpenetratingnetworks (IPN) wherein a vinyl-containing silicone fluid having aviscosity of 500 to 100,000 cS is dispersed in a conventionalthermoplastic resin. Arkles only illustrates these IPNs at relativelylow levels of silicone. The vinyl-containing silicone is vulcanized inthe thermoplastic during melt mixing according to a chain extension orcrosslinking mechanism which employs a silicon hydride-containingsilicone component. This disclosure states that the chain extensionprocedure results in a thermoplastic composition when thevinyl-containing silicone has 2 to 4 vinyl groups and thehydride-containing silicone has 1 to 2 times the equivalent of the vinylfunctionality. On the other hand, silicones which predominantly undergocrosslinking reaction result in thermoset compositions when thevinyl-containing silicone has 2 to 30 vinyl groups and thehydride-containing silicone has 2 to 10 times the equivalent of thevinyl functionality. Typical thermoplastics mentioned includepolyamides, polyurethanes, styrenics, polyacetals and polycarbonates.This disclosure is expanded by Arkles in U.S. Pat. No. 4,714,739 toinclude the use of hybrid silicones which contain unsaturated groups andare prepared by reacting a hydride-containing silicone with an organicpolymer having unsaturated functionality. Although Arkles discloses asilicone fluid content ranging from 1 to 40 weight percent (1 to 60% inthe case of the '739 patent), there is no suggestion of any criticalityas to these proportions or to the specific nature of the organic resin.

Publication WO 96/01291 to Advanced Elastomer Systems disclosesthermoplastic elastomers having improved resistance to oil andcompression set. These systems are prepared by first forming a curedrubber concentrate wherein a curable elastomeric copolymer is dispersedin a polymeric carrier not miscible therewith, the curable copolymerbeing dynamically vulcanized while this combination is mixed. Theresulting rubber concentrate is, in turn, blended with an engineeringthermoplastic to provide the desired TPE. Silicone rubber is disclosedas a possible elastomeric component, but no examples utilizing such asilicone are provided. Further, this publication specifically teachesthat the polymeric carrier must not react with the cure agent for thecurable copolymer.

Crosby et al. in U.S. Pat. No. 4,695,602 teach composites wherein asilicone semi-IPN vulcanized via a hydrosilation reaction is dispersedin a fiber-reinforced thermoplastic resin having a high flexuralmodulus. The silicones employed are of the type taught by Arkles, citedsupra, and the composites are said to exhibit improved shrinkage andwarpage characteristics relative to systems which omit the IPN.

Ward et al., in U.S. Pat. No. 4,831,071, disclose a method for improvingthe melt integrity and strength of a high modulus thermoplastic resin toprovide smooth-surfaced, high tolerance profiles when the modified resinis melt-drawn. As in the case of the disclosures to Arkles et al., citedsupra, a silicone mixture is cured via a hydrosilation reaction afterbeing dispersed in the resin to form a semi-IPN, and the resultingcomposition is subsequently extruded and melt-drawn.

U.S. Pat. No. 6,013,715 to Gornowicz et al. teaches the preparation ofTPSiV elastomers wherein a silicone gum (or filled silicone gum) isdispersed in either a polyolefin or a poly(butylene terephthalate)resins and the gum is subsequently dynamically vulcanized therein via ahydrosilation cure system. The resulting elastomers exhibit an ultimateelongation at break of at least 25% and have significantly improvedmechanical properties over the corresponding simple blends of resin andsilicone gum in which the gum is not cured (i.e., physical blends). Thisis, of course, of great commercial significance since the vulcanizationprocedure, and the cure agents required therefor, add to both thecomplexity as well as the expense of the preparation and vulcanizationwould be avoided in many applications if essentially identicalmechanical properties could be obtained without its employ.

In a copending application (Ser. No. 09/393029 filed on Sep. 9, 1999)now U.S. Pat. No. 6,281,286 we disclose that the impact resistance ofpolyester and polyamide resins can be greatly augmented by preparing athermoplastic silicone vulcanizate therefrom wherein the elastomericcomponent is a silicone rubber base which comprises a silicone gum and asilica filler and the weight ratio of the base to the resin ranges from10:90 to 35:65. Although the resulting thermoplastic materials haveimproved impact resistance, they do not exhibit sufficiently low modulusto be useful as elastomers.

While the above publications disclose the preparation of compositionsusing various thermoplastic resins as the matrix and a dispersed phaseconsisting of a silicone oil or elastomer which is dynamicallyvulcanized therein, neither these references, nor any art known toapplicants, teach the preparation of TPSiV elastomers based on polyamideresins having superior tensile and elongation properties.

SUMMARY OF THE INVENTION

It has now been discovered that TPSiV elastomers of the type describedin above cited U.S. Pat. No. 6,013,715 can be prepared from certainpolyamide resins wherein the silicone component is a base comprising adiorganopolysiloxane gum and a reinforcing filler. As in the case of theteachings of U.S. Pat. No. 6,013,715, the elastomers disclosed hereingenerally also have good appearance, have an elongation of at least 25%and have a tensile strength and/or elongation at least 25% greater thanthat of the corresponding simple (physical) blend wherein thediorganopolysiloxane is not cured. However, it has been surprisinglyfound that such properties are significantly enhanced when a minorportion of a hindered phenol compound is incorporated in theformulation. Moreover, inclusion of the hindered phenol apparently alsoresults in a lower melt viscosity of the instant thermoplastic elastomervulcanizates, as reflected by process torque measurements during mixing.This reduction is of considerable value to fabricators since theelastomers of the present invention can be more readily processed inconventional equipment (e.g., extruders, injection molders) and resultsin lower energy consumption. Furthermore, unlike the teachings ofArkles, cited supra, and others, the silicone component which isdispersed in the thermoplastic resin, and dynamically cured therein,must include a high molecular weight gum, rather than a low viscositysilicone fluid, the latter resulting in compositions having pooruniformity.

The present invention, therefore, relates to a thermoplastic elastomerprepared by

(I) mixing

(A) a rheologically stable polyamide resin having a melting point orglass transition temperature of 25° C. to 275° C.,

(B) a silicone base comprising

(B′) 100 parts by weight of a diorganopolysiloxane gum having aplasticity of at least 30 and having an average of at least 2 alkenylgroups in its molecule and

(B″) 5 to 200 parts by weight of a reinforcing filler,

 the weight ratio of said silicone base to said polyamide resin beinggreater than 35:65 to 85:15,

(C) 0.1 to 5 parts by weight of a hindered phenol compound for each 100parts by weight of said polyamide and said silicone base,

(D) an organohydrido silicon compound which contains an average of atleast 2 silicon-bonded hydrogen groups in its molecule and

(E) a hydrosilation catalyst, components (D) and (E) being present in anamount sufficient to cure said diorganopolysiloxane (B′); and

(II) dynamically curing said diorganopolysiloxane (B′),

wherein said thermoplastic elastomer has an elongation of at least 25%.

The invention further relates to a thermoplastic elastomer which isprepared by the above method.

DETAILED DESCRIPTION OF THE INVENTION

Component (A) of the present invention is a thermoplastic polyamideresin. These resins are well known by the generic term “nylon” and arelong chain synthetic polymers containing amide (i.e., —C(O)—NH—)linkages along the main polymer chain. For the purposes of the presentinvention, the polyamide resin has a melt point (m.p.) or glasstransition temperature (T_(g)) of room temperature (i.e., 25° C.) to275° C. Attempts to prepare TPSiV elastomers from polyamides havinghigher melt points (e.g., nylon 4/6) resulted in poor physicalproperties, the ultimate elongation of such products being less than therequired 25% according to the present invention. Furthermore, for thepurposes of the present invention, the polyamide resin must be dry, thispreferably being accomplished by passing a dry, inert gas over resinpellets or powder at elevated temperatures. Again, it has been foundthat TPSiVs prepared from as-supplied resins often do not meet theelongation requirements of the present invention. The degree of dryingconsistent with acceptable properties and processing depends on theparticular polyamide and its value is generally recommended by themanufacturer or may be determined by a few simple experiments. It isgenerally preferred that the polyamide resin contains no more than about0.1 weight percent of moisture. Finally, the polyamide must also betheologically stable under the mixing conditions required to prepare theTPSiV elastomer, as described infra. This stability is evaluated on theneat resin at the appropriate processing temperature and a change ofmore than 20% in melt viscosity (mixing torque) within the timegenerally required to prepare the corresponding TPSiVs (e.g., 10 to 30minutes in a bowl mixer) indicates that the resin is outside the scopeof the present invention. Thus, for example, a dried nylon 11 samplehaving a m.p. of 198° C. was mixed in a bowl mixer under a nitrogen gaspurge at about 210 to 220° C. for about 15 minutes and the observedmixing torque increased by approximately 200%. Such a polyamide resin isnot a suitable candidate for the instant method.

Other than the above mentioned limitations, resin (A) can be anythermoplastic crystalline or amorphous high molecular weight solidhomopolymer, copolymer or terpolymer having recurring amide units withinthe polymer chain. In copolymer and terpolymer systems, more than 50mole percent of the repeat units are amide-containing units. Examples ofsuitable polyamides are polylactams such as nylon 6, polyenantholactam(nylon 7), polycapryllactam (nylon 8), polylauryllactam (nylon 12), andthe like; homopolymers of aminoacids such as polypyrrolidinone (nylon4); copolyamides of dicarboxylic acid and diamine such as nylon 6/6,polyhexamethyleneazelamide (nylon 6/9), polyhexamethylene-sebacamide(nylon 6/10), polyhexamethyleneisophthalamide (nylon 6,I),polyhexamethylenedodecanoic acid (nylon 6/12) and the like; aromatic andpartially aromatic polyamides; copolyamides such as copolymers ofcaprolactam and hexamethyleneadipamide (nylon 6/6,6), or a terpolyamide,e.g. nylon 6/6,6/6,10; block copolymers such as polyether polyamides; ormixtures thereof. Preferred polyamide resins are nylon 6, nylon 12,nylon 6/12 and nylon 6/6.

Silicone base (B) is a uniform blend of a diorganopolysiloxane gum (B′)a reinforcing filler (B″).

Diorganopolysiloxane (B′) is a high consistency (gum) polymer orcopolymer which contains at least 2 alkenyl groups having 2 to 20 carbonatoms in its molecule. The alkenyl group is specifically exemplified byvinyl, allyl, butenyl, pentenyl, hexenyl and decenyl. The position ofthe alkenyl functionality is not critical and it may be bonded at themolecular chain terminals, in non-terminal positions on the molecularchain or at both positions. It is preferred that the alkenyl group isvinyl or hexenyl and that this group is present at a level of 0.001 to 3weight percent, preferably 0.01 to 1 weight percent, in thediorganopolysiloxane gum.

The remaining (i.e., non-alkenyl) silicon-bonded organic groups incomponent (B′) are independently selected from hydrocarbon orhalogenated hydrocarbon groups which contain no aliphatic unsaturation.These may be specifically exemplified by alkyl groups having 1 to 20carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl and hexyl;cycloalkyl groups, such as cyclohexyl and cycloheptyl; aryl groupshaving 6 to 12 carbon atoms, such as phenyl, tolyl and xylyl; aralkylgroups having 7 to 20 carbon atoms, such as benzyl and phenethyl; andhalogenated alkyl groups having 1 to 20 carbon atoms, such as3,3,3-trifluoropropyl and chloromethyl. It will be understood, orcourse, that these groups are selected such that thediorganopolysiloxane gum (B′) has a glass temperature (or melt point)which is below room temperature and the gum is therefore elastomeric.Methyl preferably makes up at least 50, more preferably at least 90,mole percent of the non-unsaturated silicon-bonded organic groups incomponent (B′).

Thus, polydiorganosiloxane (B′) can be a homopolymer or a copolymercontaining such organic groups. Examples include gums comprisingdimethylsiloxy units and phenylmethylsiloxy units; dimethylsiloxy unitsand diphenylsiloxy units; and dimethylsiloxy units, diphenylsiloxy unitsand phenylmethylsiloxy units, among others. The molecular structure isalso not critical and is exemplified by straight-chain and partiallybranched straight-chain, linear structures being preferred.

Specific illustrations of organopolysiloxane (B′) include:

trimethylsiloxy-endblocked dimethylsiloxane-methylhexenylsiloxanecopolymers;

dimethylhexenlylsiloxy-endblocked dimethylsiloxane-methylhexenylsiloxanecopolymers;

trimethylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxanecopolymers;

trimethylsiloxy-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers;dimethylvinylsiloxy-endblocked dimethylpolysiloxanes;

dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxanecopolymers;

dimethylvinylsiloxy-endblocked methylphenylpolysiloxanes;

dimethylvinylsiloxy-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers;and similar copolymers wherein at least one end group isdimethylhydroxysiloxy. Preferred systems for low temperatureapplications includemethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers anddiphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers,particularly wherein the molar content of the dimethylsiloxane units isabout 93%.

Component (B′) may also consist of combinations of two or moreorganopolysiloxanes. Most preferably, component (B′) is apolydimethylsiloxane homopolymer which is terminated with a vinyl groupat each end of its molecule or is such a homopolymer which also containsat least one vinyl group along its main chain.

For the purposes of the present invention, the molecular weight of thediorganopolysiloxane gum is sufficient to impart a Williams plasticitynumber of at least about 30 as determined by the American Society forTesting and Materials (ASTM) test method 926. The plasticity number, asused herein, is defined as the thickness in millimeters×100 of acylindrical test specimen 2 cm³ in volume and approximately 10 mm inheight after the specimen has been subjected to a compressive load of 49Newtons for three minutes at 25° C. When the plasticity of thiscomponent is less than about 30, as in the case of the low viscosityfluid siloxanes employed by Arkles, cited supra, the TPSiVs prepared bydynamic vulcanization according to the instant method exhibit pooruniformity such that at high silicone contents (e.g., 50 to 70 weightpercent) there are regions of essentially only silicone and those ofessentially only thermoplastic resin, and the blends are weak andfriable. The gums of the present invention are considerably more viscosethan the silicone fluids employed in the prior art. For example,silicones contemplated by Arkles, cited supra, have an upper viscositylimit of 100,000 cS (0.1 m²/s) and, although the plasticity of fluids ofsuch low viscosity are not readily measured by the ASTM D 926 procedure,it was determined that this corresponds to a plasticity of approximately24. Although there is no absolute upper limit on the plasticity ofcomponent (B′), practical considerations of processability inconventional mixing equipment generally restrict this value. Preferably,the plasticity number should be about 100 to 200, most preferably about120 to 185.

Methods for preparing high consistency unsaturated group-containingpolydiorganosiloxanes are well known and they do not require a detaileddiscussion in this specification. For example, a typical method forpreparing an alkenyl-functional polymer comprises the base-catalyzedequilibration of cyclic and/or linear diorganopolysiloxanes in thepresence of similar alkenyl-functional species.

Component (B″) is a finely divided filler which is known to reinforcediorganopolysiloxane (B′) and is preferably selected from finelydivided, heat stable minerals such as fumed and precipitated forms ofsilica, silica aerogels and titanium dioxide having a specific surfacearea of at least about 50 m²/gram. The fumed form of silica is apreferred reinforcing filler based on its high surface area, which canbe up to 450 m²/gram and a fumed silica having a surface area of 50 to400 m²/g, most preferably 200 to 380 m²/g, is highly preferred.Preferably, the fumed silica filler is treated to render its surfacehydrophobic, as typically practiced in the silicone rubber art. This canbe accomplished by reacting the silica with a liquid organosiliconcompound which contains silanol groups or hydrolyzable precursors ofsilanol groups. Compounds that can be used as filler treating agents,also referred to as anti-creeping agents or plasticizers in the siliconerubber art, include such ingredients as low molecular weight liquidhydroxy- or alkoxy-terminated polydiorganosiloxanes,hexaorganodisiloxanes, cyclodimethylsilazanes and hexaorganodisilazanes.It is preferred that the treating compound is an oligomerichydroxy-terminated diorganopolysiloxane having an average degree ofpolymerization (DP) of 2 to about 100, more preferably about 2 to about10 and it is used at a level of about 5 to 50 parts by weight for each100 parts by weight of the silica filler. When component (B′) is thepreferred vinyl-functional or hexenyl-functional polydimethylsiloxane,this treating agent is preferably a hydroxy-terminatedpolydimethylsiloxane.

For the purposes of the present invention, 5 to 200 parts by weight,preferably 5 to 150 and most preferably 20 to 100 parts by weight, ofthe reinforcing filler (B″) are uniformly blended with 100 parts byweight of gum (B′) to prepare silicone base (B). This blending istypically carried out at room temperature using a two-roll mill,internal mixer or other suitable device, as well known in the siliconerubber art. Alternatively, the silicone base can be formed in-situduring mixing prior to dynamic vulcanization of the gum, as furtherdescribed infra. In the latter case, the temperature of mixing is keptbelow the softening point or melting point of the polyamide resin untilthe reinforcing filler is well dispersed in the diorganopolysiloxanegum.

Hindered phenol (C) is an organic compound having at least one group ofthe structure

in its molecule. In the above formula, R is an alkyl group having one tofour carbon atoms and R′ is a hydrocarbon group having four to eightcarbon atoms. For the purposes of the present invention, a groupaccording to formula (i) can be attached to hydrogen to form a1,5-di-organophenol. Preferably, one to four of these groups areattached to an organic moiety of corresponding valence such that thecontemplated compound has a molecular weight (MW) of less than about1,500. Most preferably, four such groups are present in component (C)and this compound has a molecular weight of less than 1,200. Thismonovalent (or polyvalent) organic moiety can contain heteroatoms suchas oxygen, nitrogen, phosphorous and sulfur. The R′ groups in the aboveformula may be illustrated by t-butyl, n-pentyl, butenyl, hexenyl,cyclopentyl, cyclohexyl and phenyl. It is preferred that both R and R′are t-butyl.

Non-limiting specific examples of component (C) include various hinderedphenols marketed by Ciba Specialty Chemicals Corporation under thetradename Irganox™M:

Irganox™ 1076=octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate,

Irganox™ 1035=thiodiethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate),

Irganox™MD1024=1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine,

Irganox™1330=1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,

Irganox™ 1425 WL=calciumbis(monoethyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate) and

Irganox™3114=1,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione.

Preferred hindered phenols are Irganox™ 245{triethyleneglycol bis(3-(3′-tert-butyl-4′-hydroxy-5′-methylphenyl)propionate)}, Irganox™1098{N,N′-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide)}and Irganox™1010{tetrakis(methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate))methane}.

From 0.1 to 5 parts by weight of hindered phenol (C) are employed foreach 100 parts by weight of polyamide (A) plus silicone base (B).Preferably 0.1 to 0.75 parts by weight, more preferably 0.475 to 0.525parts by weight, of (C) are added for each 100 parts by weight of (A)plus (B).

The organohydrido silicon compound (D) is a crosslinker (cure agent) fordiorganopolysiloxane (B′) of present composition and is anorganopolysiloxane which contains at least 2 silicon-bonded hydrogenatoms in each molecule, but having at least about 0.1 weight percenthydrogen, preferably 0.2 to 2 and most preferably 0.5 to 1.7, percenthydrogen bonded to silicon. Those skilled in the art will, of course,appreciate that either component (B′) or component (D), or both, musthave a functionality greater than 2 if diorganopolysiloxane (B′) is tobe cured (i.e., the sum of these functionalities must be greater than 4on average). The position of the silicon-bonded hydrogen in component(D) is not critical, and it may be bonded at the molecular chainterminals, in non-terminal positions along the molecular chain or atboth positions. The silicon-bonded organic groups of component (D) areindependently selected from any of the hydrocarbon or halogenatedhydrocarbon groups described above in connection withdiorganopolysiloxane (B′), including preferred embodiments thereof. Themolecular structure of component (D) is also not critical and isexemplified by straight-chain, partially branched straight-chain,branched, cyclic and network structures, linear polymers or copolymersbeing preferred, this component should be compatible withdiorganopolysiloxane (B′) (i.e., it is effective in curing component(B′)).

Component (D) is exemplified by the following:

low molecular siloxanes, such as PhSi(OSiMe₂H)₃;

trimethylsiloxy-endblocked methylhydridopolysiloxanes;

trimethylsiloxy-endblocked dimethylsiloxane-methylhydridosiloxanecopolymers;

dimethylhydridosiloxy-endblocked dimethylpolysiloxanes;

dimethylhydrogensiloxy-endblocked methylhydrogenpolysiloxanes;

dimethylhydridosiloxy-endblocked dimethylsiloxane-methylhydridosiloxanecopolymers;

cyclic methylhydrogenpolysiloxanes;

cyclic dimethylsiloxane-methylhydridosiloxane copolymers;

tetrakis(dimethylhydrogensiloxy)silane;

silicone resins composed of (CH₃)₂HSiO_(1/2), (CH₃)₃SiO_(1/2), andSiO_(4/2) units; and

silicone resins composed of (CH₃)₂HSiO_(1/2), (CH₃)₃SiO_(1/2),

CH₃Si O_(3/2), PhSiO_(3/2) and SiO_(4/2) units,

wherein Me and Ph hereinafter denote methyl and phenyl groups,respectively.

Particularly preferred organohydrido silicon compounds are polymers orcopolymers comprising RHSiO units ended with either R₃SiO_(1/2) orHR₂SiO_(1/2), wherein R is independently selected from alkyl groupshaving 1 to 20 carbon atoms, phenyl or trifluoropropyl, preferablymethyl. It is also preferred that the viscosity of component (D) isabout 0.5 to 1,000 mPa-s at 25° C., preferably 2 to 500 mPa-s. Further,this component preferably has 0.5 to 1.7 weight percent hydrogen bondedto silicon. It is highly preferred that component (D) is selected from apolymer consisting essentially of methylhydridosiloxane units or acopolymer consisting essentially of dimethylsiloxane units andmethylhydridosiloxane units, having 0.5 to 1.7 percent hydrogen bondedto silicon and having a viscosity of 2 to 500 mPa-s at 25° C. It isunderstood that such a highly preferred system will have terminal groupsselected from trimethylsiloxy or dimethylhdridosiloxy groups.

Component (D) may also be a combination of two or more of the abovedescribed systems. The organohydrido silicon compound (D) is used at alevel such that the molar ratio of SiH therein to Si-alkenyl incomponent (B′) is greater than 1 and preferably below about 50, morepreferably 3 to 30, most preferably 4 to 20.

These SiH-functional materials are well known in the art and many ofthem are commercially available.

Hydrosilation catalyst (E) is a catalyst that accelerates the cure ofdiorganopolysiloxane (B′) in the present composition. This hydrosilationcatalyst is exemplified by platinum catalysts, such as platinum black,platinum supported on silica, platinum supported on carbon,chloroplatinic acid, alcohol solutions of chloroplatinic acid,platinum/olefin complexes, platinum/alkenylsiloxane complexes,platinum/beta-diketone complexes, platinum/phosphine complexes and thelike; rhodium catalysts, such as rhodium chloride and rhodiumchloride/di(n-butyl)sulfide complex and the like; and palladiumcatalysts, such as palladium on carbon, palladium chloride and the like.Component (E) is preferably a platinum-based catalyst such aschloroplatinic acid; platinum dichloride; platinum tetrachloride; aplatinum complex catalyst produced by reacting chloroplatinic acid anddivinyltetramethyldisiloxane which is diluted with dimethylvinylsiloxyendblocked polydimethylsiloxane, prepared according to U.S. Pat. No.3,419,593 to Willing; and a neutralized complex of platinous chlorideand divinyltetramethyldisiloxane, prepared according to U.S. Pat. No.5,175,325 to Brown et al. , these patents being hereby incorporated byreference. Most preferably , catalyst (E) is a neutralized complex ofplatinous chloride and divinyltetramethyldisiloxane.

Component (E) is added to the present composition in a catalyticquantity sufficient to promote the reaction of components (B′) and (D)and thereby cure the diorganopolysiloxane to form an elastomer. Thecatalyst is typically added so as to provide about 0.1 to 500 parts permillion (ppm) of metal atoms based on the total weight of thethermoplastic elastomer composition, preferably 0.25 to 100 ppm.

In addition to the above mentioned major components (A) through (E), aminor amount (i.e., less than about 40 weight percent of the totalcomposition, preferably less than 20 weight percent) of an optionaladditive (F) can be incorporated in the compositions of the presentinvention. This optional additive can be illustrated by, but not limitedto, reinforcing fillers for polyamide resins, such as glass fibers andcarbon fibers; extending fillers such as quartz, calcium carbonate, anddiatomaceous earth; pigments such as iron oxide and titanium oxide,electrically conducting fillers such as carbon black and finely dividedmetals, heat stabilizers such as hydrated cerric oxide, antioxidants,flame retardants such as halogenated hydrocarbons, alumina trihydrate,magnesium hydroxide, organophosphorous compounds and other fireretardant (FR) materials. A preferred FR additive is calcium silicateparticulate, preferably a wollastonite having an average particle sizeof 2 to 30 μm. Further, this optional component can be a plasticizersfor the silicone gum component, such as polydimethylsiloxane oil, and/ora plasticizer for the polyamide component. Examples of the latterinclude phthalate esters such as dicyclohexyl phthalate, dimethylphthalate, dioctyl phthalate, butyl benzyl phthalate and benzylphthalate; trimellitate esters such as C₁-C₉ alkyl trimellitate;sulfonamides such as N-cyclohexyl-p-toluenesulfonamide,N-ethyl-o,p-toluenesulfonamide and o-toluenesulfonamide, and liquidoligomeric plasticizers. Preferred plasticizers are liquids with lowvolatility to avoid emissions of plasticizer at the common melttemperatures of polyamides.

The above additives are typically added to the final thermoplasticcomposition after dynamic cure, but they may also be added at any pointin the preparation provided they do not interfere with the dynamicvulcanization mechanism. Of course, the above additional ingredients areonly used at levels which do not significantly detract from the desiredproperties of the final composition.

According to the method of the present invention, the thermoplasticelastomer is prepared by thoroughly dispersing silicone base (B) andhindered phenol (C) in polyamide (A) and dynamically vulcanizing thediorganopolysiloxane using organohydrido silicon compound (D) andcatalyst (E). For the purposes of the present invention, the weightratio of silicone base (B) to polyamide resin (A) is greater than 35:65.It has been found that when this ratio is 35:65 or less, the resultingvulcanizate generally has a modulus more resembling the polyamide resinthan a thermoplastic elastomer. On the other hand, the above mentionedratio should be no more than about 85:15 since the compositions tend tobe weak and resemble cured silicone elastomers above this value.Notwithstanding this upper limit, the maximum ratio of (B) to (A) forany given combination of components is also limited by processabilityconsiderations since too high a silicone base content results in atleast a partially crosslinked continuous phase which is no longerthermoplastic. For the purposes of the present invention, this practicallimit is readily determined by routine experimentation and representsthe highest level of component (B) which allows the TPSiV to becompression molded. It is, however, preferred that the finalthermoplastic elastomer can also be readily processed in otherconventional plastic operations, such as injection molding and extrusionand, in this case, the weight ratio of components (B) to (A) should beno more than about 75:25. Such a preferred thermoplastic elastomer whichis subsequently re-processed generally has a tensile strength andelongation which are within 10% of the corresponding values for theoriginal TPSiV (i.e., the thermoplastic elastomer is little changed byre-processing). Although the amount of silicone base consistent with theabove mentioned requirements depends upon the particular polyamide resinand other components selected, it is preferred that the weight ratio ofcomponents (B) to (A) is 40:60 to 75:25, more preferably 40:60 to 70:30.

Mixing is carried out in any device which is capable of uniformlydispersing the components in the polyamide resin, such as an internalmixer or a twin-screw extruder, the latter being preferred forcommercial preparations. The temperature is preferably kept as low aspractical consistent with good mixing so as not to degrade the resin.Depending upon the particular system, order of mixing is generally notcritical and, for example, components (A), (C) and (D) can be added to(B) at a temperature above the softening point (melt point) of (A),catalyst (E) then being introduced to initiate dynamic vulcanization.However, components (B) through (D) should be well dispersed in resin(A) before dynamic vulcanization begins. As previously mentioned, it isalso contemplated that the silicone base can be formed in-situ. Forexample, the reinforcing filler may be added to a mixer alreadycontaining the polyamide resin and diorganopolysiloxane gum at atemperature below the softening point (melt point) of the resin tothoroughly disperse the filler in the gum. The temperature is thenraised to melt the resin, the other ingredients are added andmixing/dynamic vulcanization are carried out. Optimum temperatures,mixing times and other conditions of the mixing operation depend uponthe particular resin and other components under consideration and thesemay be determined by routine experimentation by those skilled in theart. It is, however, preferred to carry out the mixing and dynamicvulcanization under a dry, inert atmosphere (i.e., one that does notadversely react with the components or otherwise interfere with thehydrosilation cure), such as dry nitrogen, helium or argon. It has beenobserved that there is actually a preferred dry gas flow rate withrespect to mechanical properties of the final TPSiV as well as the meltviscosity thereof (see examples, infra).

When the melting point or glass temperature of the polyamide isconsiderably higher than room temperature (e.g., greater than 100° C.),a preferred procedure comprises preparing a pre-mix by blending driedpolyamide resin (A), silicone base (B), hindered phenol (C) andorganohydrido silicon compound (D) below the melting point/glasstemperature of the resin (e.g., at ambient conditions). This pre-mix isthen melted in a bowl mixer or internal mixer using a dry inert gaspurge and at a controlled temperature which is just above the melt pointto about 35° C. above the melt point of the polyamide (e.g., 210° C. to215° C. for nylon 12 which, depending on molecular weight, has a meltpoint of about 175° C.-180° C.) and catalyst (E) is mixed therewith.Mixing is continued until the melt viscosity (mixing torque) reaches asteady state value, thereby indicating that dynamic vulcanization of thediorganopolysiloxane of component (B) is complete.

As noted above, in order to be within the scope of the presentinvention, the tensile strength or elongation, or both, of the TPSiVsmust be at least 25% greater than that of a corresponding simple blend.A further requirement of the invention is that the TPSiV has at least25% elongation, as determined by the test described infra. In thiscontext, the term “simple blend” denotes a composition wherein theweight proportions of resin (A), base (B) and hindered phenol (C) areidentical to the proportions in the TPSiV, but no cure agents areemployed (i.e., either component (D) or (E), or both, are omitted andthe gum is therefore not cured). In order to determine if a particularcomposition meets the above criterion, the tensile strength of the TPSiVis measured on dumbbells having a length of 25.4 mm and a width of 3.2mm and a typical thickness of 1 to 2 mm, according to ASTM method D 412,at an extension rate of 50 mm/min. At least three such samples areevaluated and the results averaged after removing obvious low readingsdue to sample inhomogeneity (e.g., such as voids, contamination orinclusions). These values are then compared to the corresponding averagetensile and elongation values of a sample prepared from the simple blendcomposition. When at least a 25% improvement in tensile and/orelongation over the simple blend is not realized there is no benefitderived from the dynamic vulcanization and such TPSiVs are not withinthe scope of the present invention.

The thermoplastic elastomer prepared by the above described method canthen be processed by conventional techniques, such as extrusion, vacuumforming, injection molding, blow molding, overmolding or compressionmolding. Moreover, these compositions can be re-processed (recycled)with little or no degradation of mechanical properties.

The novel thermoplastic elastomers of the present invention can be usedfor fabricating wire and cable insulation, electrical connectors,automotive and appliance components such as belts, hoses, air ducts,boots, bellows, gaskets and fuel line components, architectural seals,bottle closures, medical devises, sporting goods and general rubberparts.

EXAMPLES

The following examples are presented to further illustrate thecompositions and method of this invention, but are not to be construedas limiting the invention, which is delineated in the appended claims.All parts and percentages in the examples are on a weight basis and allmeasurements were obtained at 25° C., unless indicated to the contrary.

Materials

The following materials, listed alphabetically for ease of reference,were employed in the examples.

BASE 1 is a silicone rubber base made from 68.7% PDMS 1, defined infra,25.8% of a fumed silica having a surface area of about 250 m²/g(Cab-O-Sil® MS-75 by Cabot Corp., Tuscola, Ill.), 5.4% of ahydroxy-terminated diorganopolysiloxane having an average degree ofpolymerization (DP) of about 8 and 0.02% of ammonia.

BASE 2 is a silicone rubber base made from 76.6% PDMS 1, defined infra,17.6% of a fumed silica having a surface area of about 250 m²/g, 5.7% ofa hydroxy-terminated diorganopolysiloxane having an average degree ofpolymerization (DP) of about 8 and 0.02% of ammonia.

BASE 3 is similar to BASE 1 wherein only 5% of fumed silica is present.

CATALYST 1 is a 1.5% platinum complex of1,3-diethenyl-1,1,3,3-tetramethyldisiloxane; 6.0%tetramethyldivinyldisiloxane; 92% dimethylvinyl endedpolydimethylsiloxane and 0.5% dimethylcyclopolysiloxanes having 6 orgreater dimethylsiloxane units.

IRGANOX™ 245 is a hindered phenol marketed by Ciba Specialty ChemicalsCorporation, Tarrytown, N.Y., and described as triethyleneglycol bis{3-(3′-tert-butyl-4′-hydroxy-5′-methylphenyl)propionate},

IRGANOX™ 1010 is a hindered phenol stabilizer marketed by Ciba SpecialtyChemicals Corporation and described as tetrakis{methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)}methane.

IRGANOX™ 1098 is a hindered phenol described asN,N′-hexamethylene-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) andmarketed by Ciba Specialty Chemicals Corporation.

NYLON 11 is nylon 11 obtained from Aldrich Chemical Co., Milwaukee,Wis.; m.p.=198° C.

NYLON 12-A is nylon 12 obtained from Aldrich Chemical Co.; m.p.=178° C.

NYLON 12-B is Rilsan™ AMNO, a nylon 12 marketed by Elf Atochem NA, Inc.,Philadelphia, Pa.; m.p.=175° C.

NYLON 4/6 is nylon 4/6 obtained from Aldrich Chemical Co.; m.p.=295° C.

NYLON 6 is nylon 6 obtained from Aldrich Chemical Co. m p.=228.5° C.

NYLON 6/6-A is Zytel™ E42 A NC 010 nylon 6/6 obtained from DuPont;,m.p.=262° C.

NYLON 6/6-B is nylon 6/6 obtained from Aldrich Chemical Co.; m.p.=267°C.

NYLON 6/6-C is nylon 6/6 marketed by Solutia, Inc. (St. Louis, Mo.)under the tradename Vydyne™ 66B; m.p.=260° C.

NYLON 6/12 is nylon 6/12 obtained from Aldrich Chemical Co.; m.p.=218°C.

PDMS 1 is a gum consisting of 99.81 wt % Me₂SiO units, 0.16% MeViSiOunits and 0.03% Me₂ViSiO_(1/2) units, wherein Vi hereinafter representsa vinyl group. Prepared by potassium catalyzed equilibration of cyclicsiloxanes wherein the catalyst is neutralized with carbon dioxide. Thisgum has plasticity of about 150.

PDMS 2 is a gum similar to PDMS 1 but having 99.97 wt % Me₂SiO units,and 0.03% Me₂ViSiO_(1/2) units and plasticity of about 150.

PDMS 3 is a gum similar to PDMS 1 but having 97.70 wt % Me₂SiO units,2.27%

MeViSiO units and 0.03% Me₂ViSiO_(1/2) units and plasticity of about150.

PDMS 4 is a gum similar to PDMS 1 but having 87.05 wt % Me₂SiO units,12.76%

PhMeSiO units, 0.16% MeViSiO units and 0.03% Me₂ViSiO_(1/2) units andplasticity of about 150.

X-LINKER 1 is an SiH-functional crosslinker consisting essentially of68.4% MeHSiO units, 28.1% Me₂SiO units and 3.5% Me3SiO_(1/2) units andhas a viscosity of approximately 29 mPa·s. This corresponds to theaverage formula MD₁₆D′₃₉M, in which (hereinafter) M is (CH₃)₃Si—O—, D is—Si(CH₃)₂—O— and D′ is —Si(H)(CH₃)—O—.

X-LINKER 2 is a fluid similar to X-LINKER 1 having the average formulaMD₆₁D′₈M.

X-LINKER 3 is a fluid similar to X-LINKER 1 having the average formulaMD₁₀₈D′₁₀M.

X-LINKER 4 is a fluid similar to X-LINKER 1 having the average formulaMD₁₆₉D′₂₃M.

X-LINKER 5 is a fluid similar to X-LINKER 1 having the average formulaMD′₆₅M.

X-LINKER 6 is a fluid similar to X-LINKER 1 containing about 68% D′units and having a viscosity of approximately 100 mPa-s.

EXAMPLES A1-A17

NYLON 12-A (80.0 g) was dried at 120° C. for two hours in a desiccatingoven (i.e., a drying system in which hot air is dried over a desiccantbed and then passed through a heated oven containing the sample to bedried in a continuous flow cycle). This resin was then melted at 210° C.at 60 rpm in a Haake System 9000™ miniaturized internal mixer (310 mlbowl) under a dry nitrogen atmosphere using roller rotors. IRGANOX™ 1010(0.24 g) was added and mixed for approximately 3.5 minutes and then BASE1 (120.0 g) was mixed in. After about 3 minutes, X-LINKER 1 (3.8 g) wasadded, at which point the mixer torque was approximately 1,800 m-g.After another 3.5 minutes, CATALYST 1 (57 drops=0.855 g) was added andthe torque started to rise sharply. After seven additional minutes, thetorque increased to 16,400 m-g , mixing was stopped and the resultingnylon TPSiV sample was removed from the bowl.

A sample of the above material was compression molded at 225° C. for 5minutes under approximately 10 ton pressure (99 KPa) in a stainlesssteel Endura™ 310-2 Coated mold followed by cold pressing for 3 minutes.The tensile properties were measured on dumbbells having a length of25.4 mm, width of 3.18 mm and a thickness of 1 to 2 mm, according toASTM method D 412 at 23° C. and an extension rate 50 mm/min. At least 3samples were tested, the results being averaged and presented in TableA1 (Example A1). For comparison purposes, a simple physical blend (PB)having the same ratio of NYLON 12-A and BASE 1 which did not containcrosslinker or catalyst was prepared. The poor mechanical properties ofthis physical blend, also shown in Table A1, illustrate the advantage ofdynamic vulcanization (Comparative Example A2).

TPSiVs and physical blends based on various nylons at two differentlevels of hindered phenol were prepared according to the methods ofExample A1, the respective mechanical properties again being presentedin Table A1. Each such resin was processed at the temperature indicatedin the fourth column, as necessitated by the different melting points.Mixing was stopped after torque had stabilized at the value reported andsamples were molded at a temperature commensurate with the melt point ofthe particular nylon.

TABLE A1 Set IRGANOX ™ Ny- Process Elon- 1010 Content lon Temp. Tensilegation Torque Example (g) Type (° C.) (MPa) (%) (m-g) Ex. A1 0.24 12 21012.5 134 16,400  Comp. Ex. 0.24 12 210 3.1 22 1,700 A2 (PB) Ex. A3 1 12210 14.9 200 15,000  Comp. Ex. 0.24 11 215 6.44 17 12,000  A4 Comp. Ex.0.24  6/12 240 8.0 19 4,200 A5 Comp. Ex. 1  6/12 240 1.92 7 1,000 A6(PB) Ex. A7 1  6/12 240 15.8 141 3,900 Ex. A8 1  6 245 11.0 99 5,200 Ex.A9* 1  6 245 10.3 76 4,000 Ex. A10* 0.24  6 245 12.7 84 5,000 Ex. A110.24  6 245 7.74 39 8,000 Comp. Ex. 0.24  6 245 1.63 6 1,000 A12 (PB)Comp. Ex. 0.24 6/6-B 275 8.8 22 4,000 A13 Comp. Ex. 1.0 6/6-A 275 2.2 47,800 A14 Comp. Ex. 0 6/6-B 285 1.25 6 1,200 A15 (PB) Comp. Ex. 1 4/6300 5.49 10 3,800 A16 Comp. Ex. 0 4/6 300 1.3 4   800 A17 (PB) PB =Physical blend (no crosslinking) *X-LINKER 6 used instead of X-LINKER 1at same level.

As can be seen from a comparison of Examples A1 and A3, increasing thehindered phenol content resulted in improved physical properties.Further, formulations based on NYLON 11 did not result in a producthaving sufficient elongation, this polyamide exhibiting unstablerheology under these conditions. Likewise, NYLON 4/6 has a melt pointabove 275° C. and, again, resulted in poor mechanical properties even ata higher hindered phenol content.

EXAMPLES A18-A21

TPSiVs based on NYLON 12-A were prepared according to the methods ofExample A1 wherein the total amount of BASE 1 and NYLON 12-A wasmaintained at 200 g but the ratio of these two components, as well asIRGANOX™ 1010 content, were varied, as shown in Table A2. The X-LINKER 1amount was also adjusted to maintain a constant SiH/Vi ratio. Therespective mechanical properties are also presented in this table.

TABLE A2 IRGANOX ™ Ratio of 1010 Content BASE 1 to Tensile Elonga-Torque Example (g) NYLON 12-A (MPa) tion (%) (m-g) Ex. A18 0.18 70/303.14 28 13,000 Comp. Ex. 0.15 75/25 1.1 14 12,200 A19 Ex. A20 0.12 80/202.85 64 10,000 Ex. A21 0.09 85/15 3.35 116 9,000

EXAMPLES A22-A32

The above experiments were repeated using an IRGANOX™ 1010 content of 1g in otherwise similar formulations wherein the ratio of base to NYLON12-A was varied, the results being shown in Table A3

TABLE A3 IRGANOX ™ Ratio of 1010 Content BASE 1 to Tensile Elonga-Torque Example (g) NYLON 12-A (MPa) tion (%) (m-g) Ex. A22 1 60/40 14.9200 15,000 Comp. Ex. 1 60/40 2.16 15 1,500 A23 (PB) Ex. A24 1 65/35 15.7243 >19,000 Comp. Ex. 1 70/30 0.63 23 1,800 A25 (PB) Ex. A26 1 70/3011.5 119 12,000 Comp. Ex. 1 75/25 * * 2,000 A27 (PB) Ex. A28 1 75/257.94 145 14,000 Comp. Ex. 1 80/20 * * 2,200 A29 (PB) Ex. A30 1 80/208.99 229 11,000 Comp. Ex. 1 85/15 * * 2,500 A31 (PB) Ex. A32** 1 85/157.14 245 11,000 PB = Physical blend (no crosslinking) *material too weakto measure tensile properties **order of addition during mixing was:BASE 1, NYLON 12-A, IRGANOX ™1010 and X-LINKER 1 followed by CATALYST 1.

From Tables A2 and A3 it is again apparent that physical blends whereinthe silicone component is not cured do not meet the minimal requirementsof elongation for TPSiVs of the present invention. Although thecompositions of Examples A30 and A32 could be compression molded, it wasobserved that these could not be extruded. Thus, as discussed above,such TPSiVs having a weight ratio of base to polyamide greater thanabout 75:25 are less preferred. Further, this series is illustrative ofthe type of routine experimentation required to determine the lowerlimit of hindered phenol required to attain at least a 25% elongationfor a given system.

EXAMPLES A33-A38

TPSiVs based on dried NYLON 12-A were prepared according to the methodsof Example A1 wherein the effects of drying the nylon resin, use of apurge and inclusion of IRGANOX™ 1010 were evaluated. In this series ofexperiments, the proportions of the components and bowl filling factor(i.e., the percent of bowl free-volume occupied by the ingredients) weremaintained as in Example A1 but mixing was carried out in a 60 mlminiaturized internal mixer so that reported torque values are not to becompared with those obtained with the 310 ml bowl. The results arepresented in Table A4, wherein the second column indicates whetherdrying of the nylon (120° C./2hr) was employed, whether dry nitrogen wasapplied and whether IRGANOX™ 1010 (0.24 parts per 200 parts of NYLON12-A+BASE 1) was included (indicated by + in each case) and when not(indicated by − in each case).

TABLE A4 Drying/Nitrogen/ Tensile Elongation Torque Example IRGANOX ™1010 (MPa) (%) (m-g) Comp. Ex. −/−/+ 5.0 21 550 A33 Ex. A34 +/−/+ 6.6735 550 Ex. A35 +/+/+ 13.6 115 >3,150 Comp. Ex. −/−/− 4.96 15 650 A36Comp. Ex. −/+/− 5.77 19 3,200 A37 Comp. Ex. −/+/+ 2.58 14 1,200 A38

It is clear from Table A4 that the combination of drying, dry nitrogenpurge and inclusion of IRGANOX™ 1010 provides the best mechanicalproperties.

EXAMPLES A39-A43

TPSiVs based on dried NYLON 12-B were prepared according to the methodsof Example A1 wherein the flow rate of dry nitrogen to the mixer wasvaried. The results are shown in Table A5, wherein the flow rate isreported in m³/min.

TABLE A5 Nitrogen Flow Tensile Elongation Torque Example (m³/min) (MPa)(%) (m-g) Ex. A39 0.028 13.6 180 >20,000 Ex. A40 0.014 14.6 217 11,000Ex. A41 0.0071 16.2 274 11,000 Ex. A42 0.0028 15.6 233 15,800 Ex. A43 09.57 70 1,800

It can be seen that the sample prepared without the nitrogen purge(Example A43) had relatively poor mechanical properties, although withinthe requirements of the invention. Additionally, there is an apparentoptimum nitrogen flow rate with respect to good mechanical propertiesand low process viscosity (i.e., low torque).

EXAMPLES A44-A51

NYLON 6/6-B (80.0 g) was dried at 120° C. for two hours in a desiccatingoven (i.e., hot air is dried over a desiccant bed and then passedthrough a heated oven containing the sample in a continuous flow cycle).The resin was melted at 275° C. at 60 rpm in a Haake System 9000™miniaturized internal mixer (310 ml bowl) under a dry nitrogenatmosphere using roller rotors. BASE 1 (120.0 g) was added 4 minutesafter addition of polyamide. IRGANOX™ 1010 (1.0 gram) was added 2.5minutes later and mixed for approximately 2.5 minutes. X-LINKER 1 (3.8g) was added, at which point the mixer torque was approximately 1,100m-g. After another 3.5 minutes, CATALYST 1 (57 drops=0.855 g) was addedand the torque started to rise. After 18 additional minutes, the torqueincreased to 5,800 m-g , mixing was stopped and the resulting nylonTPSiV sample was removed from the bowl. The resulting TPSiV was moldedat 285° C. and tested, as described above, the results being shown inTable A6 (Example A44).

Similar compositions were prepared using NYLON 6/6-A and NYLON 6/6-C,these results also being presented in Table A6. In these examples theorder of mixing was varied, as shown in the second column of Table A6,wherein N, Irg. and Base denote the nylon, IRGANOX™ 1010 and BASE 1,respectively.

TABLE A6 Order of Torque Tensile Elongation Example addition (m-g) NylonType (MPa) (%) Ex. A44 N/Base/Irg. 5,800 NYLON 6/6-B 14.6 81 (Comp.)N/Irg./Base 8,000 NYLON 6/6-A 5.57 10 Ex. A45 A46 Base/Irg./N 10,200NYLON 6/6-A 8.70 26 (Comp.) Base/N/Irg. 7,300 NYLON 6/6-A 5.41 9 Ex. A47Ex. A48 N/Irg./Base 8,400 NYLON 6/6-C 9.33 33 (Comp.) Base/Irg/N 10,600NYLON 6/6-C 7.66 23 Ex. A49 (Comp.) N/Base/Irg. 9,800 NYLON 6/6-C 7.4516 Ex. A50 (Comp.) Base/N/Irg. 15,000 NYLON 6/6-C 6.86 14 Ex. A51

Table A6 illustrates our observation that it is more difficult toprepare TPSiVs having high tensile/elongation properties as the meltingpoint of the polyamide approaches 275° C. Nevertheless, routineexperimentation does provide compositions within the scope of thepresent invention.

EXAMPLES B1

NYLON 12-B was dried at 120° C. for 18 hours in a dessicating oven, asdescribed above in Example A1. A pre-mix of this dried polyamide wasprepared by blending the following components in a Haake Rheomix™ 3000mounted on a PolyLab™ miniaturized internal mixer using sigma bladerotors (free volume=541 cm³):

210.4 g BASE 1

6.60 g X-LINKER 1

1.75 g IRGANOX™ 1010

140.0 g NYLON 12-B

Blending was carried out at 20° C. and a rotor speed of 60 rpm, until astable torque reading was observed. The resulting pre-mix (210.8 g) wasfed to a Rheomix™ 3000 bowl fitted with roller rotors (free volume=310cm³) at 210° C., 60 rpm using a dry nitrogen purge at a flow rate of 0.5standard cubic feet per minute (236 cm³/s). As previously noted, mixingtorques observed in this series should not be compared with thoseobtained using the above described Haake System 9000™ mixer. The settemperature was reduced to 200° C. and when the mixing torque began tolevel out, indicating that the nylon had melted and the pre-mix hadreached the set temperature, 57 drops (0.912 g) of CATALYST 1 wereadded. When the torque again reached a steady state value (5,800 m-g),the resulting TPSiV was removed.

The above product was compression molded at 225° C. for 5 minutes andexhibited a tensile strength of 2631 psi (18.1 MPa) and an elongation of298% according to ASTM method D 412, as described in Example A1 with theexception that at least 5 tensile measurements were averaged.

EXAMPLES B2-B5

The procedures of Example B1 were followed wherein NYLON 12-A served asthe polyamide resin and the type of hindered phenol was varied. In eachcase, 120.0 g of the polyamide, 80.0 g of BASE 1 and 3.8 g of X-LINKER 1were pre-mixed using sigma blades. This premix was dynamically cured byadding 1 g of the hindered phenol indicated in Table B1 and 0.912 g ofCATALYST 1. This table also shows the respective mechanical propertiesof molded test specimens.

TABLE B1 Ultimate Tensile Hindered Terminal Strength Elongation atExample Phenol Torque (m-g) (MPa) Break (%) Ex. B2 IRGANOX ™ 7,150 16.2251 1010 Ex. B3 IRGANOX ™ 9,090 16.3 237 245 Ex. B4 IRGANOX ™ 10,00013.2 151 1098 Comp. Ex. none 10,000 12.2 134 B5

It can be seen from Table B1 that omitting the hindered phenol reducesultimate mechanical properties.

EXAMPLES C1-C4

Nylon TPSiVs were prepared according to the methods of Example B1wherein different siloxane gums having various vinyl contents were used.In each case, the respective gum shown in Table C1 was used in place ofPDMS 1 in the formulation of BASE 1 to prepare a similar silicone base,the latter then being used in the following proportions to provide thefinal TPSiV:

NYLON 12-A 80 g IRGANOX ™ 1010 1 g SILICONE BASE 120 g X-LINKER 1 3.8 gCATALYST 1 0.86 g

TABLE C1 Vinyl Content of Gum Tensile Elongation Torque Example Gum (wt%) (MPa) (%) (m-g) Ex. C1 PDMS 2 0.012 10.9 100 12,000 Ex. C2 PDMS 10.0652 13.7 170 22,000 Ex. C3 PDMS 3 0.753 10.8 39 6,000 Ex. C4 PDMS 40.0596 14.5 193 15,000

EXAMPLES C5-C7

Nylon TPSiVs were prepared according to the methods of Example C1wherein different silicone bases having various levels of silica fillerwere used. In each case, the respective base shown in Table C2 was usedin the following formulation to provide the final TPSiV:

NYLON 12-A 80 g IRGANOX ™ 1010 1 g SILICONE BASE 120 g X-LINKER 1 3.0 gCATALYST 1 0.86 g

TABLE C2 Tensile Example Silicone Base (MPa) Elongation (%) Torque (m-g)Ex. C5 BASE 1 13.5 160 17,500 Ex. C6 BASE 2 10.9 107 11,000 Ex. C7 BASE3 4.11 30 1,800

An attempt was made to prepare a TPSiV according to the methods ofExamples C5-C7 wherein the silicone component did not contain fumedsilica (i.e., only PDMS1 gum) but the resulting composition was too weakto test.

EXAMPLES C8-C12

Nylon TPSiVs were prepared according to the methods of Example C1wherein different SiH-functional crosslinkers were used at a constantSiH/SiVi ratio. The type and amount of crosslinker employed being shownin the second and third columns of Table C3, respectively.

TABLE C3 Cross- Crosslinker linker Tensile Elongation Torque ExampleType Amount (g) (MPa) (%) (m-g) Ex. C8 X-LINKER 1 1.0 7.97 81 4,600 Ex.C9 X-LINKER 2 7.1 5.23 47 5,100 Ex. C10 X-LINKER 3 9.1 5.75 56 5,300 Ex.C11 X-LINKER 4 6.4 5.22 38 5,600 Comp. Ex. X-LINKER 5 0.66 3.15 15 4,400C12

From Table C3 it is seen that X-LINKER 1 provides the best overallmechanical properties while X-LINKER 5 is does not meet the requirementsof the invention under the conditions of this series of experiments.

What is claimed is:
 1. A method for preparing a thermoplastic elastomer,said method comprising: (I) mixing (A) a rheologically stable polyamideresin having a melting point or glass transition temperature of 25° C.to 275° C., (B) a silicone base comprising (B′) 100 parts by weight of adiorganopolysiloxane gum having a plasticity of at least 30 and havingan average of at least 2 alkenyl radicals in its molecule and (B″) 5 to200 parts by weight of a reinforcing filler,  the weight ratio of saidsilicone base to said polyamide resin being greater than 35:65 to 85:15,(C) 0.1 to 5 parts by weight of a hindered phenol compound for each 100parts by weight of said polyamide and said silicone base, (D) anorganohydrido silicon compound which contains an average of at least 2silicon-bonded hydrogen groups in its molecule and (E) a hydrosilationcatalyst, components (D) and (E) being present in an amount sufficientto cure said diorganopolysiloxane (B′); and (II) dynamically curing saiddiorganopolysiloxane (B′), wherein at least one property of thethermoplastic elastomer selected from tensile strength or elongation isat least 25% greater than the respective property for a correspondingsimple blend wherein said diorganopolysiloxane is not cured and saidthermoplastic elastomer has an elongation of at least 25%.
 2. The methodaccording to claim 1, wherein the weight ratio of said silicone base (B)to said polyamide resin (A) is greater than 35:65 to 75:25.
 3. Themethod according to claim 2, wherein said polyamide is selected from thegroup consisting of nylon 6, nylon 6/6, nylon 6/12 and nylon
 12. 4. Themethod according to claim 2, wherein said diorganopolysiloxane (B′) is agum selected from the group consisting of a copolymer consistingessentially of dimethylsiloxane units and methylvinylsiloxane units anda copolymer consisting essentially of dimethylsiloxane units andmethylhexenylsiloxane units and said reinforcing filler (B″) is a fumedsilica.
 5. The method according to claim 4, wherein said organohydridosilicon component (D) is selected from the group consisting of a polymerconsisting essentially of methylhydridosiloxane units and a copolymerconsisting essentially of dimethylsiloxane units andmethylhydridosiloxane units, having 0.5 to 1.7 weight percent hydrogenbonded to silicon and having a viscosity of 2 to 500 mPa-s at 25° C. andsaid catalyst (E) is a neutralized complex of platinous chloride anddivinyltetramethyldisiloxane.
 6. The method according to claim 3,wherein the weight ratio of said silicone base (B) to said polyamideresin (A) is 40:60 to 70:30.
 7. The method according to claim 2, whereinsaid hindered phenol has a molecular weight of less than 1,200 andcontains 2 to 4 groups of the formula

in which R and R′ are tert-butyl groups.
 8. The method according toclaim 4, wherein said fumed silica is present at a level of 20 to 100parts by weight for each 100 parts by weight of saiddiorganopolysiloxane (B′).
 9. The method according to claim 8, whereinsaid polyamide resin is selected from the group consisting of nylon 6,nylon 6/6, nylon 6/12 and nylon
 12. 10. The method according to claim 9,wherein said hindered phenol is selected from the group consisting oftriethyleneglycol bis(3-(3′-tert-butyl-4′-hydroxy-5′-methylphenyl)propionate),N,N′-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) andtetrakis(methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate))methane.11. The method according to claim 10, wherein the weight ratio of saidsilicone base (B) to said polyamide resin (A) is 40:60 to 70:30.
 12. Themethod according to claim 4, wherein said polyamide has a melt pointgreater than 100° C. and wherein a pre-mix of components (A) through (D)is first prepared at a temperature below the melting point of thepolyamide, said catalyst (E) is subsequently added to said pre-mix at atemperature above the melt point and said diorganopolysiloxane (B′) isthen dynamically vulcanized.
 13. A thermoplastic elastomer prepared bythe method of claim
 1. 14. A thermoplastic elastomer prepared by themethod of claim
 2. 15. A thermoplastic elastomer prepared by the methodof claim
 3. 16. A thermoplastic elastomer prepared by the method ofclaim
 4. 17. A thermoplastic elastomer prepared by the method of claim5.
 18. A thermoplastic elastomer prepared by the method of claim
 6. 19.A thermoplastic elastomer prepared by the method of claim
 7. 20. Athermoplastic elastomer prepared by the method of claim
 8. 21. Athermoplastic elastomer prepared by the method of claim
 9. 22. Athermoplastic elastomer prepared by the method of claim
 10. 23. Athermoplastic elastomer prepared by the method of claim
 11. 24. Athermoplastic elastomer prepared by the method of claim 12.